The invention relates to a process for treatment of CO-rich gases incurred in the manufacture of phosphorous, which contain impurities like water, sulfur compounds, nitrogen compounds and phosphorus compounds.
Large-scale elementary phosphorous manufacture uses an electric arc with coke and gravel to convert apatites or phosphorites (e.g. Ullmann's Encyclpedia of Industrial Chemistry, 1979, Volume 18, pp. 288--292.) After leaving the converter, the waste gases pass through an electrostatic gas purification system in which approximately 98% to 99% of the dust particles are deposited. The gas primarily contains CO, but also contains impurities like sulfur compounds, nitrogen compounds, phosphorus compounds and carbon dioxide due to secondary reactions in the furnace. In the conventional process, the gas substantially freed of dust, is now introduced into a condensation system. Subsequently, the gas is directly cooled with water to facilitate phosphorus extraction from the gas stream to the greatest possible extent. The waste gas still contains phosphorous corresponding to the temperature of the process water. However, this process does not permit a very thorough cleaning of the gas as the solubilities of the impurities contained therein are too different. For instance, the poor solubilities of phosphine and phosphorous prohibits a simple cleaning by a physical scrub.
It is known to convert phosphorus and phosphorus compounds with concentrated sulfuric acid but this process entails formation of other components, as for instance, sulfur dioxide which is undesirable and in further reuse may cause water waste and environmental problems. Thus, after the sulfuric acid scrub, in which the phosphorus components are removed, another scrub for removal of existing and newly formed acid components is necessary.
Due to the complex and costly purification of such gases, it has been preferred practice up to now, to use combustion for disposal of such gases whereby the phosphorus and sulfur components caused environmental pollution. Also, in most cases, combustion of CO is unsatisfactory from an economic standpoint as there is a demand for CO, and obtaining CO by conversion of hydrocarbons (e.g. natural gas, naptha or coal) is a costly process.
It is the objective of the invention to present a process which treats CO rich gases incurred in the manufacture of phosphorus, which contain impurities like water, sulfur compounds, nitrogen compounds and phosphorus compounds in simple and cost-effective manner, thus simultaneously permitting product recovery of CO without incurring environmentally harmful byproducts.
It is another object of the invention to provide a process for the recovery of purified CO from CO-rich gases yielded during production of phosphorus, the CO-rich gases containing impurities consisting essentially of H.sub.2 O, H.sub.2, N.sub.2, O.sub.2 +Ar, CH.sub.4, PH.sub.3, CO.sub.2, COS, H.sub.2 S, HCN, and P.sub.4, comprising; cooling the CO-rich gases in regenerators to separate the impurities from a CO product stream, wherein the impurities are frozen or condensed within the generators, and withdrawing from the regenerators a CO product stream, wherein the steps of cooling and withdrawing further comprise passing the CO-rich gases through a first generator, wherein the impurities are frozen or condensed and a cold CO product stream is withdrawn, and wherein the first regenerators is pressurized, expanding a second regenerator to remove CO product stream generated from a previous step of passing CO-rich gases therethrough, and separating a partial CO product stream from the CO product stream, cooling a third regenerator by passing the cold CO product stream therethrough, wherein the CO product stream is recovered after passing through the third regenerator, and purging a fourth regenerator with the partial CO product stream after passing the partial CO product stream through an expansion turbine to lower the temperature of the partial CO product stream, and cyclically repeating the above steps so that each regenerator undergoes, in order, the steps of passing through the CO-rich gases, then expanding, then cooling, and then purging.